A power supply apparatus to be incorporated in an air conditioning apparatus, heat source apparatus, and the like includes a rectifier circuit configured to rectify voltages of an AC source, booster circuit configured to boost an output voltage of the rectifier circuit, and inverter configured to convert an output voltage of the booster circuit into AC voltages of a predetermined frequency, and drives a compressor motor of a refrigerating cycle in the air conditioning apparatus or heat source apparatus by using the output of the inverter.
The booster circuit described above is a so-called boost chopper including a series circuit of a reactor and first switch element to be connected to output ends of the above rectifier circuit, diode for backflow prevention provided in a current path between the first switch element and load (aforementioned inverter), and capacitor or the like connected in parallel with the load, boosts the output voltage of the rectifier circuit by repeating turning on/off of the first switch element, and outputs the output voltage of the rectifier circuit without boosting the output voltage by continuously keeping the first switch element in the off-state.
In a power supply apparatus provided with such a booster circuit, control is carried out in such a manner that when the load is increased and an effective value of an input current flowing into the booster circuit rises to a value greater than or equal to a set value (state where the counter-electromotive force of the compressor motor increases to such an extent that inverter control for increasing the rotational speed of the compressor motor reaches a maximum), boosting of the booster circuit is started and, when the load is decreased and the effective value of the input current flowing into the booster circuit lowers to a value less than the set value, boosting of the booster circuit is stopped. As the aforementioned set value, each of a second set value for a boosting start and first set value for a boosting stop lower than the second set value is used. A difference between the second set value and first set value is a hysteresis width used to prevent frequent repetitions of a boosting start and boosting stop from occurring.
In order to reduce switching loss of the booster circuit to the extent possible, it is advisable to make the first set value for a boosting stop close as possible to the second set value for a boosting start. By making the first set value close to the second set value, the timing of the boosting stop is brought forward, and the period of boosting is reduced correspondingly, whereby it is possible to reduce the switching loss (for example, JP 2010-187521 A).
However, when the magnitude of the input current flowing into the booster circuit of the case where the AC source voltage or frequency is in an unbalanced state at the time of boosting is compared with the magnitude thereof at the time of non-boosting, the magnitude at the time of non-boosting is greater than the magnitude at the time of boosting under the same load conditions.
Accordingly, when setting is made in such a manner that the first set value is close to the second set value, if the AC source is in the unbalanced state, at the time of a boosting stop, the effective value of the input current rises immediately after the boosting stop, and the effective value reaches the second set value for a boosting start, whereby boosting is immediately started. That is, a stop of boosting and start of boosting are repeated within a short period of time. This adversely affects the lifetime of each electronic component of the booster circuit.